Answer to Question #8406 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Space Flight

The following question was answered by an expert in the appropriate field:


Do astronauts have lead in their suits to protect them from cosmic radiation? If they don't use lead, what do they use? If they do, is lead shielding effective to stop cosmic radiation?


The cosmic radiation environment is actually fairly complex—it includes UV (ultraviolet), x rays, and gamma rays. But the most significant radiation comes in the form of particles—protons, electrons, and high-energy helium atoms that have been stripped of their electrons (also called helium nuclei or alpha radiation). Some of these can be shielded; others cannot.

UV, potentially life-threatening, is fairly easily shielded by covering up. The visors are treated to reflect UV, and the opaque layers of the suit take care of the rest. On the other extreme, x rays and gamma rays are hard to shield—this is where the lead would come in, but there is not enough of this form of radiation to make the extra weight worthwhile. The lead apron a radiologist wears can weigh 10–15 kg, so lining the entire suit with this thickness of lead would add at least 25–40 kg to a suit that is already bulky and heavy. The material of the suit itself attenuates some of this radiation, but this is not the primary risk to astronauts.

The remaining types of radiation are different kinds of atomic or subatomic particles. These are far and away the most common and the most damaging types of radiation—they come mostly from the sun. Luckily, most of them are not very penetrating (alpha particles, for example, cannot even punch through a sheet of paper). So the great majority of this radiation is stopped by the ordinary construction of the suit and it is not a problem. The little bit that's left is so energetic and so hard to shield that, as with gamma rays, it's not worth trying to shield against it. I should also point out that, in near-Earth orbit, the Earth's magnetic field provides very high levels of protection against charged particles—they are more or less herded into the Van Allen radiation belts that surround our planet. As long as astronauts are working at lower altitudes, they also enjoy this protection.

So, we have several kinds of radiation that are fairly easily shielded (UV, most particles) and that are the most potentially dangerous. And the kinds of radiation that are the hardest to shield (x ray, gamma ray, and the highest-energy particles) are generally not as great a risk.

Andrew Karam, CHP


Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
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